1. Field of Invention
The invention relates to a device and process for electrolytic deposition of metals on one or both sides of strips which form the cathode, preferably steel strips.
2. The Prior Art
In horizontal or vertical galvanic systems of this type, the deposition of metals from the electrolyte takes place on strips which form the cathode, which pass through two anodes which are parallel to one another and insoluble. An electrical charge, generally rectified, is applied to the two anodes, so that the metallic precipitation on the strip passing through takes place under the known suitable conditions. Such a system is known, for example, from DE-OS 35 10 592. Such and similar devices are also used, however, for one-sided coating of the strip passing through. One of the two parallel anodes is then removed from the device. Since systems generally have several pairs of anodes arranged one after the other, through which the strip passes, this results in long setup times of the system for one-sided coating. In addition, it is frequently found that in spite of the absence of the removed anode, partial coating takes place on the side of the strip which is not supposed to be coated.
Attempts have also already been made, in order to avoid such setup times, to have no current or voltage applied to one of the two anodes in each case. In operation, however, it turns out that in such a case, a disruptive metal precipitation on the anode takes place, both on the side of the strip which is not supposed to be coated, and in the lower anode region. Depending on the anode material, e.g. in the case of iridium dioxide coated anodes, this causes the surface to be passivated in the lower region and therefore to become unusable. The explanation must obviously be seen in the fact that a voltage drop from the entry point to the exit point of the segment of the strip to be coated takes place, so that potential differences between the anode, which actually has no current applied to it, and the strip segment opposite it occur, which are obviously sufficient to trigger deposition processes in the direction of the anode and/or the strip.
It has therefore already been proposed that the current-free anode be insulated from the strip segment by intermediate placement of an insulation, for example a thin plastic sheet. However, it is frequently not possible to place such insulation sheets in the very narrow gap between the strip and the anode. Furthermore, such a measure also requires significant setup times when switching from two-side coating operation to one-sided coating operation and vice versa.